Conventionally, there is known an internal combustion engine that promotes combustion of an air fuel mixture utilizing an electromagnetic wave. For example, Patent Document 1 discloses an internal combustion engine of this kind.
The internal combustion engine disclosed in Patent Document 1 includes an ignition device that causes a plasma discharge to occur by emitting a microwave in a combustion chamber before or after ignition of an air fuel mixture. The ignition device generates local plasma by discharge at an ignition plug so that the plasma is generated in a high pressure field, thereby growing the plasma by the microwave. The local plasma is generated at a discharge gap between a tip end part of an anode terminal and a ground terminal part.